How should the wind speed of the air shower be selected?

The selection of air velocity for the material air shower is a key factor in ensuring its dust removal efficiency and meeting the standards of the clean area. It needs to be determined by comprehensively considering multiple factors such as industry requirements, particulate matter control targets, and equipment parameters. The following is the detailed selection logic and reference standards: 1. The relationship between wind speed and dust removal efficiency: The core role of wind speed.
The cargo shower chamber uses high-speed air flow to impact the surface of the goods and utilizes the principles of aerodynamics to peel off and carry away dust, hair, fibers, and other particles. When the wind speed is insufficient, the kinetic energy of the airflow is not enough, making it difficult to effectively remove the firmly adhering particles. If the wind speed is too high, it may lead to increased energy consumption, noise pollution, and even damage to light goods such as packaging films and loose materials. The critical air velocity, a key parameter for dust removal efficiency, usually refers to the minimum air velocity that can effectively remove particles larger than 0.5μm, and it generally needs to be ≥20m/s. Recommended air velocity range: According to industry standards, the recommended air velocity for most scenarios is 20-25m/s. In high-cleanliness demand scenarios (such as semiconductors and pharmaceuticals), it can be increased to 25-30m/s. Ii. Core Influencing Factors for Wind Speed Selection n1. Industry Cleanliness Standards nIndustry Type Clean Area Level nRecommended Wind Speed (m/s) nCore Requirements nSemiconductor/Microelectronics noISO 5 (Class 100) and above n25-30 Control for particles under 0.1μm Strong airflow is required for GMP A/B grades of pharmaceutical/biological products 22-28 to prevent microbial contamination. Take into account the sterilization of equipment, food/health products, ISO 7-8 grade (10,000 grade / 100,000 grade), 20-25, remove dust and allergen particles, precision machinery/aviation, ISO 6-7 grade (1,000 grade / 10,000 grade, 20-22, prevent contamination by large particles such as metal debris. 2. Goods characteristics, material, and surface area: Rough surfaces (such as wooden crates, and woven bags) require a higher wind speed (above 25m/s) to penetrate the gaps. For smooth surfaces (such as metal containers), a speed of 20-22m/s can be adopted. For goods with large surface areas (such as palletized stacked materials), the wind speed or the number of nozzles needs to be increased to ensure full coverage of the airflow. Weight and stability of goods: For light goods (such as cartons and foam packaging), it is recommended that the wind speed be ≤22m/s to avoid being blown over by the air current. The wind speed can be appropriately increased for heavy goods. 3. Characteristics of Particulate Matter: Particle size and density: For dust particles under 0.5μm, a wind speed of ≥25m/s is required (the airflow has strong inertia and is easy to capture tiny particles). Large particles (such as dust and hair larger than 10μm) can be removed by a wind speed of 20m/s. Particle adhesion strength
Oily and wet particles (such as processing oil stains and dust adhering to condensate water) require a higher wind speed (25-30m/s) in combination with nozzle Angle optimization (such as 45° oblique blowing). 4. Equipment Parameters and Energy Consumption Nozzle Design:
Wind speed is related to the number of nozzles, aperture and Angle (for example, if the coverage area of the fan-shaped nozzle is large, the wind speed needs to be ≥22m/s;) The wind speed of the circular nozzle can be ≥25m/s. Fan power and energy consumption:
For every 10% increase in wind speed, energy consumption increases by approximately 20%. A balance needs to be struck between efficiency and cost, for instance, by using variable frequency fans (which can adjust the wind speed as needed and save about 30% of energy). Iii. Specific Steps for Selecting Air Velocity Determine the clean area grade and particle control targets by referring to industry standards (such as GMP, ISO 14644), and clearly define the particle size to be controlled (such as 0.3μm, 0.5μm) and concentration limits. Evaluate the type of goods and loading method. Record the size, material, and stacking density of the goods. If it is multi-layer shelves or dense loading, increase the wind speed to more than 25m/s to ensure the penetration of airflow. The formula for calculating the base wind speed and air volume is: (v = frac{Q}{A}) (where v is the wind speed, Q is the air volume, and A is the cross-sectional area of the cargo shower chamber). For example, the dimensions of the air shower are 2m×1.5m×2.5m (length × width × height), with A cross-sectional area of (A = 1.5×2.5 = 3.75m²). If a wind speed of 25m/s is required, then the air volume (Q = 25×3.75×3600 = 337500m³/h). In combination with the adjustment of equipment configuration, if the number of nozzles is small (such as single-sided blowing), the wind speed needs to be increased by 10%-20%. If the air is blowing from both sides or three sides, it can be designed according to the standard wind speed. After the installation of the testing and optimization equipment, use a dust particle counter to detect the particle concentration before and after the material spray. If the dust removal efficiency is less than 99% (i.e., the decrease in particle count is less than 99%), increase the wind speed by 1-2m/s and try again. Iv. Common Misunderstandings and Precautions: Higher is not always Better: Wind speed greater than 30m/s may cause airflow disorder, generating vortices that carry particle diffusion instead, and noise greater than 75dB (A) requires additional noise reduction treatment. Dynamic balance design: If the opening frequency of the material shower room is high (such as ≥10 times per hour), a wind speed compensation mechanism (such as automatic speed increase by a variable frequency fan) should be set up to avoid positive pressure imbalance in the clean area. Maintenance impact: After long-term operation of the fan, dust accumulation on the impeller will cause a decrease in wind speed (about 5%-10% per year). It is recommended to calibrate with an anemometer every quarter and clean the fan and filter if necessary. V. Industry Typical Case Reference: Semiconductor wafer factory: 0.1μm particles need to be controlled. A 30m/s air velocity + HEPA filter (filtration efficiency ≥99.99%@0.3μm) is adopted, and a rotating tray is used to blow the goods 360°. Baking food factory: For flour dust, a 22m/s air velocity + medium-efficiency filter (F8 grade) is adopted, and an anti-dust accumulation design is added at the nozzle. Medical device factory: GMP Class B clean area, air velocity 25m/s + ultraviolet sterilization lamp, ensuring that the number of particles after material spray is ≤100 per cubic meter (above 0.5μm). Through comprehensive design from the above dimensions, it is possible to achieve a balance between high efficiency and energy conservation in the air velocity of the material shower room while meeting the cleanliness standards.